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How to do Temperature Mapping for Warehouse Qualification

A material storage area or warehouse is often a second-tier priority in a biopharma project. Unlike process areas, the environmental requirements are much more relaxed–no air changes or room pressures or particle counts to worry about. Compared to process areas, the temperature and humidity can vary over a wider range: 15-25 C and less than 60%, respectively.

But the story gets a little complicated as these areas require temperature mapping, an activity that can be challenging and time-consuming if not planned and executed well. This post takes a shot at temperature mapping by addressing the following questions:

  1. What is temperature mapping? And why do we need it?
  2. How to do it?
  3. Which pitfalls to avoid?

1. What’s temperature mapping and why

Used for the bulk storage of temperature-sensitive materials, a warehouse comes with the following unique features:

  • Big area with a high ceiling
  • Multi-tier racks for storing pallets
  • Frequent door openings to transfer materials
  • The inflow of materials at different temperatures (e.g., from ambient temperature)

Considering the usage and features of a warehouse, the uniformity and stability of temperature and relative humidity (RH) become the key requirements. And that’s where enters the temperature mapping into the story.

Temperature mapping helps:

  • to verify that temperature and RH are within the acceptable range across the whole volume of a warehouse;
  • to verify the stability of these parameters over a period of days; and
  • to identify the hot (warmest) and cold (coldest) spots in the whole warehouse.

Next, let’s see how to do it.

2. How to map

“How” itself is a big question with the following sub-questions:

  • How many loggers are required? And where do you place them?
  • What kind of loggers are acceptable?
  • When should temperature mapping be done? And what’s the duration of mapping?

How many loggers and their locations

To decide on the number of loggers and their locations, we need two inputs:

  1. Warehouse details
    • A set of drawings showing the warehouse dimensions (length, width, height), placement of racks (number of rows, length, height and tiers), locations of HVAC supply air outlets, location of controlling thermostat (if it is in the room) and locations of doors.
  2. Guidelines for loggers’ locations
    • Horizontal distance between loggers: 5–10 meters
    • Height: If the ceiling height is 3.6 meters or less, position loggers in three layers: lowest, middle and highest to cover the whole material storage space, say, at 0.3 m, 1.8 m and 3.3 m (highest storage point). If the ceiling height is more, say 6.0 m, place loggers in four layers, covering the lowest, lower middle, higher middle and highest storage levels.
    • Doors: Place a logger near the door to capture the impact of door openings.
    • Corners: All corners need to be covered.
    • HVAC outlet: Avoid placing loggers in front of HVAC supply air grilles/diffusers.
    • Controlling thermostat: If there is a controlling thermostat, place a logger nearby.

(Note: First two items come from WHO’s Supplement 8: Temperature mapping of storage areas, May 2015. Read it if you wish to dive deeper into temperature mapping.)

With the two inputs in hand—warehouse details and guidelines–it’s not difficult to come up with a mapping layout that would look something like the drawing below.

Example of Temperature Mapping Layout

What type of loggers

We need loggers with a good storage capacity that can capture both temperature and RH. Three parameters are important for logger selection: Range, accuracy and resolution. Here are some typical values:

Temperature

  • Range: – 20 C to +55 C
  • Accuracy: +/-0.5 C
  • Resolution: 0.1 C

Relative humidity

  • Range: 0-100%
  • Accuracy: +/- 2%
  • Resolution: 0.1% RH

In addition, two more things are important:

  • Calibration of loggers: 3-point calibration covering the range of measurements
  • Sampling rate of data collection: 5 min (typical)

When and how long to map

Typically, the mapping is done during Operational Qualification and Performance Qualification (PQ), but in my opinion, it should also be done during commissioning. If any problem is there in terms of either temperature/RH uniformity or stability, you don’t want to discover it during OQ. To summarize the phases and durations of mapping:

  • Commissioning (optional but highly recommended): 24-hour mapping | empty chamber (no load)
  • OQ: 24-hour mapping | empty chamber
  • PQ: 3-day or 7-day mapping | loaded chamber (75-80% occupied)

For places with seasonal variations (summer & winter), the mapping will need to be repeated to cover both seasons. (That’s not the case with Singapore where I am writing this post.)

3. Pitfalls to avoid

Finally, what are some of the pitfalls to avoid creating a monster out of the temperature mapping exercise?

Screwing the design: If the design is flawed, by the time project reaches the mapping stage, it’s too late to fix the mess. While designing, better to be conservative. The target design values should be tight: 21 +/- 2 C and 55 +/- 5% or even more conservative: 50 +/-5%).

Rushing the commissioning: In many projects, people are infatuated with the mapping exercise and try to push for it without ensuring proper commissioning of the HVAC system. That’s a recipe for a mess during qualification.

Selecting an inexperienced vendor for mapping: Choosing a reliable and cooperative vendor with proven experience is eventually cheaper than opting for an inexperienced but cheaper vendor.

Not keeping quality guys in the loop: Mapping is the key activity for warehouse qualification. Keeping the quality team in the loop at every stage, especially while finalizing the mapping layout, will save you from surprises later on.

Working with half-baked warehouse design drawings: The mapping layout should be prepared with the final construction or as-built drawings.

Not studying the international and internal guidelines: Anyone leading this exercise should study all the relevant international and internal guidelines and SOPs.

Note: I’ve purposefully not included things like logger identification, mapping report, placement of EMS sensors based on hot and cold spots, etc. Don’t want to make it too long.

Finally, leaving you with a point to ponder:

While deciding on mapping layout, what do you about the areas where materials are not going to be stored–aisles and passageways? Map these areas as well or only focus on the material storage areas (racks)?

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